The invention relates to improvements in cutting tools useful for cutting slots in work pieces and is more particularly concerned with improved cutting tools for gear cutting operations.
It is known in the art of gear cutting to provide for cutting tools formed from lengths of bar stock which can be easily resharpened by their users by simply regrinding top and flank surfaces on a profiled cutting end of each tool. The cutting face of such a tool does not require resharpening, and this permits a preservation of the cutting face for metallurgical or other types of treatments which improve cutting and wear characteristics of the tool. In addition, it is known to provide compound front cutting faces on such tools which extend parallel to the tool axis and which may be either angularly related or offset with respect to each other. Cutting faces may extend either the full length of the tool or part of that length. In the latter instance, the tool may include a rectangular cross-section in its base portion, and this provides for better mounting and increased rigidity of the tool when mounted in a cutter head.
Typically, gear cutting tools are arranged in groups about a cutter head. Each group may include separately designed cutting tools for separately cutting the two side walls and the bottom portion of each tooth slot to be formed in a work piece. For instance, an inside cutting tool may be provided to cut one side wall of a tooth slot, an outside cutting tool may be provided to cut the opposite side wall of the same tooth slot, and a bottom cutting tool may be provided for forming the bottom of the tooth slot in the work piece. The bottom cutting tool, however, may be eliminated if inside and outside cutting tools are appropriately designed with compound front cutting faces for cutting portions of the bottom of a tooth slot. By providing inside and outside tools with compound cutting faces in lieu of bottom cutting tools, associated second top and flank surfaces on these tools may be more effectively utilized. Normally, second top and flank surfaces are provided only for cutting clearance purposes. However, cutting tools with compound cutting faces may be designed so that second top and flank surfaces on these tools perform a rough cutting function. More particularly, inside and outside tools with compound cutting faces may be designed so that each tool finish cuts one side wall and a portion of the bottom of a tooth slot as well as rough cuts the opposite side wall and remaining bottom portion of the same tooth slot. In this way a greater number of tools can be provided in a given cutter head for working the side walls of the tooth slots being formed and this provides for faster completing operations in which tooth slots are formed in a single set up between tooling and work piece. Also, in certain gear cutting operations such as continuous index cutting, it is especially difficult to accurately position bottom cutting tools, and thus, their elimination greatly simplifies the design and set up of this type of cutter assembly.
Gear cutting tools generally consist of hardened tool steel with front cutting faces ground into the tool steel with a rotary disk shaped grinding wheel. For forming a first cutting face in a length of bar stock, a disk shaped grinding wheel may be adapted to traverse across the bar stock with respect to its lengthwise direction. In this way a first cutting face may be formed in part of the length of the bar stock while maintaining a base portion of rectangular cross section in the remaining length of the bar stock. The base portion includes rectangular mounting surfaces which are useful for locating the tool during subsequent formation of the cutting end of the tool and for rigidly mounting the tool within a cutter head during use. Preferably, an abrupt junction is formed between the first cutting face and base portion of the tool so that the useful lengths of both the cutting face and base portion may be maximized. For forming offset or certain angularly related second front cutting faces, a disk shaped grinding wheel must traverse along the length of the bar stock instead of across the same length to prevent removal of the first formed cutting face. Lengthwise grinding of the second cutting face, however, prevents formation of an abrupt junction between the cutting face and the base portion of the tool. Typically, either an impression of the circumference of a disk shaped grinding wheel is formed in the region of this junction or a section of the base portion of the tool which is aligned lengthwise with the second cutting face is removed altogether. In either case, a critical corner defined between rectangular mounting surfaces at the junction of the base portion with the second cutting face may be undesirably removed. Effective use of the base portion to accurately retain the tool during subsequent manufacture and use is thereby diminished.